Transforming a paper-like model into a 3d model
Try to get front, back, top, bottom, left, and right reference images of things and making them background images with N panel N > Background Images. Make a 2D mesh for each reference and then try to combine them together to make a 3D mesh. I cannot tell you how exactly because it will vary with each model, but I can tell you that you can do CTRLJ to join the meshes and try to combine the appropriate vertices, and then fill in the faces.

I did this for a hawk's beak recently. What I did was that I made the side reference mesh, duplicated and made them 45 degrees apart (the front reference showed this), joined and connected them and made faces, applied a subsurf modifier, and it looked like an actual beak. So that tells you that this technique works. There are other methods, though!